CARTAGENA, Colombia - Prime Minister Stephen Harper says the full cost of his government's plan to purchase the F-35 stealth fighters has been "well known" for some time, but the final figure depends on what you're counting.

Answering questions at a news conference following the close of the Summit of the Americas, Harper said he's always been clear about the jets $9-billion acquisition cost. But he denied Canadians were misled about the purchase in the run-up to the last spring's federal election.

"There's more than one number, there's more than one cost depending upon what you are counting," Harper said.

Earlier this month, auditor general Michael Ferguson ignited a political firestorm when he released a report suggesting the Conservatives and the Defence Department hid the true cost of the radar-evading jet that the military claims will be critical to national sovereignty in the future.

One of the auditor's biggest complaints was that the Defence Department did not include the anticipated $10 billion life-time operating cost in its public pitch for the aircraft.

The exclusion of figures such as pilots' salaries, fuel and consumable spares, is a long-standing practise at the Defence Department — something previous auditors-general have complained about.

The Harper government and defence officials have long touted the price tag as $14.7 billion, but Ferguson put the projected 20-year cost of the program, including maintenance, at closer to $25 billion.

More importantly, the auditor said the cabinet must have known the full price tag before the last election, which was precipitated in part by the refusal of the Conservatives to provide the House of Commons with figures related to the program.

"The numbers you talk about are different numbers costing different things," Harper said on Sunday.

"The number I have talked about is the number we have budgeted for the acquisition of the F-35. And I've been very clear, those budgetary numbers are the numbers under which we are going to live."

The opposition parties have accused the Conservatives of lying to taxpayers.

Both the Liberals and the NDP are demanding a special House of Commons inquiry into the auditor's report and the military's plan to buy 65 of the advanced fighters, a U.S. program that has been hammered with cost overruns and delays.

Liberal MP Gerry Byrne and the three New Democrat MPs on the public accounts committee asked for an emergency meeting, even though Parliament is in recess until next week.

The Liberals have also launched a petition calling on the government "to tell the truth" about the fighter jet program.

Last week, Defence Minister Peter MacKay said his department will, from now on, include the operating costs in public statements of its planned purchases.